The PCR Genotyping Core involves all genotyping procedures needed for QTL mapping once the behavioral, pharmacological and neurochemical data have been collected and genomic DNA samples extracted as part of other components. This Core is central to the major theme of QTL mapping, and is required to meet almost all of the Specific Aims in Research Components 3,4 and 7. Genomic DNA will be extracted from spleen except when genotyped animals are needed as breeders, then tail tip samples will be used. Each genotyping involve the determination of which alleles an individual mouse possesses at one microsatellite marker locus, and is accomplished by a single PCR reaction. Genotyping many individuals for many markers is required for QTL confirmation and mapping in segregating (noninbred) populations where each mouse is a unique genotype. Over the 5-year period of requested support, we propose to genotype 5 B6D2F2 populations (92 mice each), 6 selection line F2 populations (80 mice each), 8 selection lines (30 mice each), 8 inbred strains ancestral to the selection liens (5 mice each), 3 phenotypic selected lines (160 mice each), eight sets of genotypic selection lines (144 mice each) and develop 16 congenic strain sets by seven generations of backcrossing (25 mice per set per generation). The grand total for the requested 5-year period of support is 52,000 PCR reactions. This Core will be functional in all years of requested Center funding.